The present study will examine familial aggregation patterns of several prominent deficits seen in autistic individuals. The aim of the study is to identify behavioral markers more proximal to the underlying gene(s) involved in autism than the clinical syndrome itself. recent research indicates that autism is familial, occurring more frequently in families of autistic children than in the general population. The familial recurrence risk of impairments more general than autism itself is even higher. Several studies have reported an increased rate of cognitive and linguistic deficits in siblings of autistic children However, these results may reflect a heritable component of mental retardation that is largely independent of autism. Indeed, when family data is stratified by IQ of the proband, familial clustering of cognitive impairment occurs only in families of retarded autistic children. It is not clear what deficit, if any, aggregates in the families of nonretarded autistic individuals. The family risk study presented here will examine cognitive, linguistic and social abilities in the siblings of autistic probands and the siblings of controls matched on age, sex, SES, ethnicity and Verbal and Performance IQ. This design will allow on examination of what might be inherited in autism when the potentially confounding effects of retardation are controlled. When the groups are matched on IQ, it is hypothesized that the rate of cognitive and linguistic abnormalities will be equivalent in the two groups, while the rate of social deficits will be elevated in the siblings of children with autism, but not in the siblings of controls.